This invention relates to drive system for a vehicle, and more particularly, to a fluid drive system incorporating a variable speed transmission.
In general, it is well known to provide a drive for a lift truck which includes an internal combustion engine connected to a two-speed manual shift transmission coupled with an oil clutch. It will be understood that while such a drive system is relatively efficient in operation, it is always desirable to achieve more efficient application of engine power and easier, and more precise control of the vehicle's motion, at a low cost. For this purpose, it would clearly be desirable to provide a fixed displacement fluid pump in combination with a fixed displacement fluid motor and further in combination with reasonably-priced means for providing an infinitely variable transmission for highly efficient driving of the vehicle.
It has been found that automatic and hydrostatic transmissions, each providing a plurality of speeds, increase overall operating efficiency of the vehicle, but at a relatively high cost.
U.S. Pat. No. 2,716,357 discloses an infinitely variable transmission of the general type utilized in the present invention, and U.S. Pat. No. 2.786,363 provides an in-depth study of the theoretical basis for such an infinitely variable transmission. The teachings of these patents are hereby specifically incorporated by reference.
U.S. Pat. No. 3,005,562 discloses a hydraulic drive for a lift truck incorporating a pressure-sensitive valve for varying the displacement of the motors for driving the truck.